Great to hear you're getting into snowboarding. This is my first season, and I'm loving it. Having made a move from the South (Florida) up North, I definitely understand the gaining weight part, especially during the winter. Between the cold weather and shorter days, I was much less active, and even though snowboarding probably isn't the best calorie burning activity in the world, winter sports in general got me out of the house and increased my energy level 10-fold. The sport definitely has a steep learning curve, though. My first few times out, my day always ended because I was just too sore to keep going. One day, though, everything seemed to just click. And although I'm certainly not shredding the slope at Mach 2 or doing 720s in the terrain park, I actually feel comfortable on the board, which is a great feeling.
Best of luck. These guys have been a great help to me, and it sounds like they're giving you some good advice.